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Space Science

Meteorite from Mercury? 16

Posted by michael from the long-way-from-home dept.
texchanchan writes "The BBC reports that a chunk of rock, clearly from space, might have originated on Mercury. Analysis of its chemical makeup leads to this tentative conclusion. Specifically, it seems to have originated on something with 'a core of molten iron [and] an outer covering of silicon and aluminium that formed a basaltic crust.' This meteorite classification site sticks to the earlier theory that NWA 011 is from a Vesta-like source."
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Meteorite from Mercury? More

Meteorite from Mercury?

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  • Am I missing something??? (Score:2, Interesting)

    by cp99 ( 559733 )
    The BBC article has very few details, so I tried to track down more information on it. I found a recent paper in Science which appears to be about this meteorite (Yamaguchi et al, Science 2002, vol. 296).

    However, in the article there is no claim to it coming from Mercury (rather it is a new type of basalt). Am I missing somebody else's intrepetation of the data, or is this media spin?
    • The abstract [sciencemag.org] of the article in Science doesn't mention Mercury either. (Nosy free registration required.) I don't know where the BBC got the idea. It would be cool (hot) if it was true, but don't know who originated it. Another note [skyandtelescope.com] about the meteorite, referring to "another Vesta," but not Mercury.
      • The impression I got from the BBC article was that the meteorite came from a body considerably larger than Vesta. I'm not sure how that oxygen-isotope thingy they're talking about works, but if it's deficient in the chunkier elements, that would imply - to my mind - that it came from a big-assed body. If that's the case - and we can assume it's not from the moon or Mars - then it must've come from a really big asteroid, or from Mercury.

        So people're inferring that it's from Mercury through a process of elimination. Seems reasonable to me.
        • Why emilinate a larger asteroid? The asteroid belt constantly has collisions and destruction of the objects. It's actually easy to imagine that there were once much larger asteroids in the belt, and they have since been shattered.

          I find it easier to believe than to believe that a rock was blasted off of Mercury and then somehow made it to Earth's orbit.

          If you really want to know where it came from, we'll need a close look at Mercury. Last I heard, the European Space Agency's Mercury mission included a lander, so we might be in luck.
          • Why emilinate a larger asteroid?
            The very nature of the asteroid belt is such that huge asteroids are unlikely (note: IANAA). Jupiter's gravitational influence would stop bodies of sufficient size from forming; loose agglomerations are possible - even likely - but these wouldn't, TTBOMK, be sufficiently packed for their own gravity to allow the iron to sink into the centre.
            • Sorry, but nope. Several asteroids where are now in the belt are massive enough to be spherical (that's a self-gravity effect) and be differentiated, Ceres and Vesta amoung them. Since we get metallic and stony meteorites on Earth, we know that some large asteroids which were differentiated must have existed only to be blown appart in a large collisions. Since we know that this erosion has been happening, there is no real reason to assume that the current asteroids are the largest that have ever existed. In fact, I can see a case that it is unlikely that Ceres is the largest asteroid to ever inhabit the asteroid belt. (Without knowing how much destruction has happened, I couldn't say off-hand.)

              Note: I am an astronomer :-)
              • Funny... I always thought Ceres was much smaller than that. And if one can be that big now, I can't in all honesty argue that there weren't bigger ones in the past. Bugger.

                Now all I need to do is try to be happy that I've been corrected rather than disgruntled at having my spurious pontification shown to be in error in front of millions of erudite personages.
                No, wait... only /. readers know I'm an idiot. Hooray!
  • OK, when the "Mars meteorite" was announces a few years ago I could possible see how they could claim to know that it originated from the 4th planet. We've send a few space probes to Mars and have been able to study (at least remotely) the make-up of certain regions on that planet. But to say that this chunk of rock is from Mercury is a bit of a streatch, IMHO. Those minerals are also abundant in asteroids. It's times like these that showcase how boundless our ignorance of our own solar system truly is.
  • Oooh, this chunk of rock came from Mars! This one's from Mercury! Hey, this one's from the planet KRYPTON! (is it green or red I wonder?)

    All this stuff seems to be based on what Frazer called "the magical laws of similarity and contagion" rather than real science. I tried to link Frazer's magnum opus The Golden Bough here but /. wouldn't take the huge bn.com link.

    It's a logical fallacy to assume that object A was once a part of object B simply because they share the same composition; in fact it's a bad idea to blindly assume object A came from B even if A is identical to an object you know came from object B!

    Pseudo-scientific psychobabble by fuzzy thinkers in search of grant money? Or just bad reporting?
    • Huh? This sounds like basic inductive logic to me. While you're right that just because a meteor shares the same composition as a planet doesn't necessarily mean it came from that planet, it's certainly suggestive that it is. Each planet has an isotope signature from one another. That is to say that in the example given mercury has a different ratio of one Oxygen isotope to another. These ratios AFAIK are consistant among the entire planetary body, and are not random. On the earth Oxygen-16 accounts for 99.76% of all oxygen atoms, where Oxygen-17 accounts for .4% of all oxygen atoms. On mercury this ratio is presumably different. If you measure a meteorite sample and it's similar in isotope ratios to that of mercury, you can reasonably conclude that the sample probbably came from mercury. If you do further analysis and find many other isotope ratios that are the same as they are on mercury, it becomes increasingly likely that your rock is really from mercury. This is not pseudo-science at all, though from reading the article the hypothesis that the rock is from mercury is still pretty tentative. You may be right that this rock may not be from mercury, but your larger scale attack on the basis of isotope composition tying rock samples to certain planets is pretty flimsy.
      • Let me highlight some of your comment to make my point:
        . If you measure a meteorite sample and it's similar in isotope ratios to that of mercury, you can reasonably conclude that the sample probbably came from mercury. If you do further analysis and find many other isotope ratios that are the same as they are on mercury, it becomes increasingly likely that your rock is really from mercury. This is not pseudo-science at all, though from reading the article the hypothesis that the rock is from mercury is still pretty tentative.

        You see, you're not committing the error I'm harping on. You described a hypothesis as likely, which is appropriate given your understanding of the data. You haven't stated a tentative hypothesis as though it were a known fact, and you've given independently verifiable background information to support your theories.

        A creationist (one of those people who thinks G-d likes to torment his creations by playing tricks on them) would say that the rock was composed as it is in order to test the faithful. This worldview is as internally consistent as your own, and it's even harder to refute.

        A person who believes in an unbounded universe could point out, postulating that infinity is real and not a mathematical conceit, that the rock could've come from a mercury-like planet in another galaxy, and the circumstances of it's transit here caused it to arrive at a time and place consistent with rocks being ejected from Mercury. Again, this is a difficult argument to comprehensively refute, since the concept of infinity expressed as a physical construct requires all things to exist.

        But regardless of which religion or philosophy one chooses, stating that it's from Mercury because Mercury is (astronomically speaking) close by and rocks on mercury are identical in composition is simply invoking the time-worn laws of similarity and contagion - the same laws behind the construction of voodoo dolls.

        Anyone really capable of deeper comprehension than these surface issues will use less absolute terms - as you did, in your post. Tying the origin of rock samples to certain planets on the basis of isotope composition is logically weak, and thus should always be stated equivocally.

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